Hudson Bruce S
Department of Chemistry, Syracuse University, Syracuse, NY 13244-4100, USA.
Materials (Basel). 2018 Feb 6;11(2):242. doi: 10.3390/ma11020242.
Polyacetylene, the simplest and oldest of potentially conducting polymers, has never been made in a form that permits rigorous determination of its structure. polyacetylene in its fully extended form will have a potential energy surface with two equivalent minima. It has been assumed that this results in bond length alternation. It is, rather, very likely that the zero-point energy is above the Peierls barrier. The experimental studies that purport to show bond alternation are reviewed and shown to be compromised by serious experimental inconsistencies or by the presence, for which there is considerable evidence, of finite chain polyenes. In this view, addition of dopants results in conductivity by facilitation of charge transport between finite polyenes. The double minimum potential that necessarily occurs for polyacetylene, if viewed as the result of elongation of finite chains, originates from admixture of the 1¹A ground electronic state with the 2¹A excited electronic singlet state. This excitation is diradical (two electron) in character. The polyacetylene limit is an equal admixture of these two ¹A states making theory intractable for long chains. A method is outlined for preparation of high molecular weight polyacetylene with fully extended chains that are prevented from reacting with neighboring chains.
聚乙炔是最简单且最古老的潜在导电聚合物，但从未以能严格确定其结构的形式制备出来。完全伸展形式的聚乙炔将具有一个具有两个等效极小值的势能面。人们一直认为这会导致键长交替。然而，零点能很可能高于派尔斯势垒。对那些据称显示键交替的实验研究进行了综述，结果表明这些研究因严重的实验不一致性或因存在（有大量证据表明）有限链多烯而受到影响。按照这种观点，掺杂剂的加入通过促进有限多烯之间的电荷传输而导致导电性。如果将聚乙炔视为有限链伸长的结果，那么必然会出现的双极小势源自1¹A基态电子态与2¹A激发单重态电子态的混合。这种激发具有双自由基（双电子）的性质。聚乙炔极限是这两个¹A态的等量混合，这使得长链的理论处理变得棘手。本文概述了一种制备具有完全伸展链且能防止与相邻链反应的高分子量聚乙炔的方法。
